She has caught 186 of London’s wildest cats – in buses, behind a Chinese supermarket and across 800 acres of industrial wasteland that is to be levelled and reshaped into the 2012 Olympic Park.

Now, with only days remaining before she must pack up her traps and make way for the builders, Celia Hammond – Sixties model turned stray cat-catcher extraordinaire – may have finally met her match.

“Time is running out,” she said, screeching to a halt outside the vast building site in a van packed with traps and cat food. “I have a horrible feeling this one’s going to beat me.”

Ms Hammond has 40 years’ experience of trapping strays. She has the patience to sit in her van for 12 hours through the night, like a surveillance officer on a stakeout, watching a baited cage. She has expended vast funds, she has a network of informers – security guards mostly – who feed her news of his movements, but still he eludes her.

He is Blackjack, cat No 187, the last cat on the Olympic Park.

Blackjack has been there since last July when Ms Hammond was called in by the London Development Agency to deal with a litter of kittens in a former industrial unit.

“We could see lots of other cats hanging around,” she said. It soon became clear that the deserted neighbourhoods were home to huge colonies of cats.

At least 40 were living behind a Chinese supermarket, feasting on rotten prawn crackers. Scores were inside a former gospel church, dozens more occupied Forman’s Salmon Curers. A large group roamed the overgrown allotments, another occupied a travellers’ site. In an old garage, cats rode stationary buses.

In almost all these places Ms Hammond and her team saw a large black long-haired tom, whom she christened Blackjack because of his “rakish character” and his propensity to take risks. “I have never known a cat cover such a huge area,” she said. “We would get a phone call saying, ‘Blackjack was here’ but when we arrived he would be gone.”

Despite Blackjack and the great colonies of cats that remained to be caught, last August the site was handed over to the Olympic Delivery Authority and Ms Hammond was ordered off.

She mounted a campaign: 15,000 cat lovers signed a petition asking for her to be allowed back to rescue the cats before they were buried beneath the rubble. Perhaps mindful that to build the Olympic Park over the bodies of cats did not send out the desired message of the 2012 Games, the authority relented and allowed Ms Hammond to return. She was eventually given until April 24 to clear the site of cats.

There have been some notable successes. George, an “incredibly wild” ginger tom, was caught on an old bus. He thrashed around wildly in captivity.

“Three days later we caught a tamer tabby cat in another bus garage,” Ms Hammond said. “She looked like a former pet. We were short of space so we put them together, and it was like the Sunsilk commercial. She completely tamed him, they snuggled up together.”

The Celia Hammond Animal Trust has rehomed three quarters of the 186 cats: some are now pets while some were too wild and have gone to farmyards and stables.

Blackjack, however, has been sighted again and again but never caught. “Everyone says I should just leave it,” Ms Hammond said. “But of all the cats I have saved, the one I remember is the one I can’t catch.

“If only I could convey to him that I’m trying to help him.”

She hopes that he might still escape the site on his own, but she cannot be sure. At the end of the month the authority will review her access and she fears she will be ordered to leave.

She will redouble her efforts in the remaining days, but it seems likely that Blackjack will remain at large and elusive – like the vanishing spirit of an older, wilder East London.

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